Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output and a flow of exhaust gases. The exhaust gases can include a complex mixture of air pollutants produced as byproducts of the combustion process. And, due to increased attention on the environment, the amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes utilizing an exhaust gas recirculation (EGR) circuit. EGR circuits operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture, when ignited, produces a lower combustion temperature and a corresponding reduced amount of regulated pollutants.
An exemplary turbocharged engine implementing exhaust gas recirculation is disclosed in a technical article titled “Engine Gas Recirculation: Internal engine technology for reducing nitrogen oxide emissions” by MTU Friedrichshafen GmbH that published in August of 2011 (“the technical article”). In particular, the technical article discloses an internal combustion engine having a plurality of cylinders arranged into two different banks. Both banks of cylinders are provided with compressed air from a three-turbocharger arrangement (i.e., a high-pressure turbocharger and parallel low-pressure turbochargers). One of the banks of cylinders discharges exhaust to the turbochargers, while the other bank is considered a donor bank and discharges exhaust for recirculation within the engine. A single EGR cooler is mounted to the top of the engine for cooling exhaust from the donor bank of cylinders before the exhaust is distributed to all cylinders for subsequent mixing with air and combustion. A first control valve is located upstream of the EGR cooler and used to control EGR flow rates, while a second control valve is located in a bypass and used to selectively direct excess exhaust from the donor bank of cylinders to the turbochargers.
Although the exhaust system of the technical article may provide for reduced emissions in some applications, it may still be less than optimal. In particular, because exhaust gas is only distributed to the different banks of cylinders from a location downstream of the EGR cooler and EGR control valve, these components may be relatively large and difficult to package. For example, the single large EGR cooler mounted to the top of the engine may be cumbersome and limit applicability. In addition, the number of control valves used by the system may increase cost and control complexity of the engine. Further, the location of the EGR control valve upstream of the cooler may create an extreme environment for the control valve that can lead to excessive wear and premature failure of the valve.
The disclosed exhaust system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.